An unusual dinosaur from Utah’s Cretaceous period has been categorized as a new genus, offering a new portrait of two distinct dinosaur communities in what is now the western United States.

Described in a study published in the current issue of Proceedings of the Royal Society B, Nasutoceratops titusi, or "big-nose, horn-face," is named for its most significant features: the two enormous horns protruding from its head and its prodigious snout. It the first from the group of short-frilled, horned dinosaurs to have been found in the American south, revising previous theories that those dinosaurs lived only in the north.

“It’s not every day you find a whole new group of dinosaurs,” says Scott Sampson, a paleontologist at The Denver Museum of Nature & Sciences and the lead author on the study, in a phone interview. “And this is a linchpin to demonstrate that there were distinct dinosaur communities in the north and south.”

Nasutoceratops’s nose is the biggest of that of any known dinosaur in the triceratops family, to which this new species belongs. But the part of the nose that is enlarged is not related to its sense of smell, and scientists are still unsure how its size benefited the animal, Sampson said.

Still, scientists are fairly confident that the humongous horns – the largest in the family in relative terms, as the Nasutoceratops’s five-foot-long head is about half the size of that of other dinosaurs in the group – were used for mating purposes.

“The horns were not used to beat up on predators,” said Dr. Sampson. “The horns were to compete for mates to attract members of the opposite sex, and to intimidate or possibly fight members of the same sex.”

Like other dinosaurs in the triceratops family, the quadrupedal herbivore, which measured about 15 feet and weighed some 2 tons, has a frill on its head, like a misshapen halo backlighting its face.

In addition to adding a bizarre new creature to the dinosaur roster, the find also adds new evidence to the idea that the western edge of what is now the United States and Canada was once home to two contemporaneous communities of dinosaurs.

The story begins at the Grand Staircase-Escalante Monument area in Utah, where the Nasutoceratops fossil was recovered in 2006. Some 75 million years ago that now arid landscape was thick with greenery and girdled with marshes. That region is known as southern Laramidia, the westernmost island that resulted when elevated sea levels during the Late Cretaceous period split the North American landmass into separate islands.

Almost all the dinosaurs found in southern Laramidia are of a different species than their family counterparts in the north. The addition of the Nasutoceratops to the Cretaceous period ecosystem in the south now adds one more species to the list of novel dinosaurs that lived there.

Scientists now believe that northern and southern horned dinosaurs diverged geographically and then evolved at the same time but separately from each other for about one million years. The results of that separate evolution were distinct dinosaur species: the horned dinosaurs in northern Laramidia developed fancy frills, with huge, boney knobs protruding from their halos, and small horns on their heads. Their southern counterpart, Nasutoceratops, has a less ornate frills and massive horns very unlike those found in that subfamily.

Much is still unknown about why the north and south dinosaurs did not intermingle, especially in such a small plot of land.

“We’re not sure that was stopping those Utah dinosaurs from migrating north and replacing the Alberta dinosaurs,” said Mark Loewen, a paleontologist at the Natural History Museum of Utah and a co-author on the study.

One possibility is differences in vegetation between the two areas, said Loewen, noting that planet preferences could have led the dinosaurs to stay in their locale.